The present invention relates generally to high-frequency electromagnetic field shielding apparatus and, more particularly, to a door assembly in a construction for substantially preventing the transition of interference fields, in particular of high-frequency electromagnetic fields, into a space.
Still more particularly, the present invention relates to a door assembly in a construction for preventing the transition of interference fields into a space which includes a door pivotally mounted to a stationary structure by at least one hinge means and wherein at least one of the door and the stationary structure is provided with means for producing an interference field transition preventing contact.
Constructions are known for providing an interference-protected or shielded space for preventing the penetration or transition of external electromagnetic energy into the protected space or, on the other hand, for confining electromagnetic energy within the space enclosed by the construction by preventing leakage of the interference field to the surrounding environment. Such prior art constructions are commonly used in order to protect sensitive equipment from electromagnetic radiation and for allowing measurements to be taken in an environment which is free from radio-frequency interference. Such constructions are generally used in industries which employ data communication and high-frequency technology in research as well as in other applications such, for example, as in hospitals.
Regardless of the particular purpose to which the protective space is put, the region of the construction providing the poorest attenuation of the interference fields is generally the zone of contact between the openable door, window, gate or the like, which is required for providing access into the protected space, and the associated stationary structure. In order to avoid deterioration of the protective properties of the door assembly, an electrical contact is provided between the movable door and the stationary door frame structure. Such electrical contact between the movable door and the stationary structure and, in the case where protection from low-frequency magnetic fields is also desired, the reluctance path between the door and the stationary structure, must be as continuous as possible and correspond to the attenuation properties of the remainder of the construction.
The attenuating properties of the contact region between the door and the stationary door frame structure can be improved, especially in the protection against transition of high frequency fields, by means of a labyrinth structure provided at the contact zone. Thus, in order to guarantee a reliable and continuous contact, knife-shaped contact tongues provided on the door are pressed between associated contact springs fitted in a groove which passes around the door opening defined by the stationary structure.
The performance of conventional door assemblies of the type described above has been limited, however, by the fact that it has not been possible to provide a multiple labyrinth structure providing the necessary tight tolerances while at the same time retaining the normal ease of operation of the door inherent in hinged door constructions. Thus, when an efficient and complicated labyrinth construction is utilized, the seal construction tends to be damaged during the pivoting movement of the normally hinged door in combination with the tight tolerances of the contact tongues penetrating between the contact springs. Thus, as the door is moved in a pivotal movement path, the contact tongues tend to pry the seal springs out of position. Moreover, the closing of the door requires an extremely high compression force which may range between 300 to 400 kp.